C# MVC/API - 从 Amazon S3 为我的 API 调用返回一个图像

Question

我正在使用 .net core 从私有 Amazon S3 存储桶上传和检索图像。

我能够成功上传它，甚至在我从 S3 下载它之后查看它，但是当我有点不确定如何将流/响应返回给客户端以进行实际的 API 调用时（例如现在我只是想使用 Postman/Fiddler 代理工具从我的 API 中取回图像）

我用于 S3 检索流的代码：

///Retrieve my image from my bucket

public async Task<string> ReadObjectData(MediaFolder key, String fileName)
    {
        string responseBody = "";
        IAmazonS3 client;

        using (client = new AmazonS3Client(accessKey, accessSecret, endpoint))
        {
            Amazon.S3.Model.GetObjectRequest request = new Amazon.S3.Model.GetObjectRequest
            {
                BucketName = bucket,
                Key = key + "/" + fileName,
            };
            using (GetObjectResponse response = await client.GetObjectAsync(request))
            using (Stream responseStream = response.ResponseStream)
            using (StreamReader reader = new StreamReader(responseStream))
            {
                string title = response.Metadata["x-amz-meta-title"];
                responseBody = reader.ReadToEnd();
            }
        }
         return responseBody;
    }

所以现在在我的控制器中，我有以下操作：

   [HttpGet("ProfilePic")]
    public async Task<IActionResult> GetProfilePicture()
    {
        var user = await GetUserFromBearerToken();

        //Retrieve
        var utf8ImageResponse = await _fileService.ReadObjectData(MediaFolder.Profiles, user.ProfileImageFileName);

        //To return a file as a stream
        var imageBytes = System.Text.Encoding.UTF8.GetBytes(utf8ImageResponse);

        //Return the image, which I'll hardcode as jpeg for a test
        return File(imageBytes, "image/jpeg");
    }

当我使用 Postman 进行调用时，它会返回一个小的空白框（如果您尝试返回图像，则会看到该框，但它在某些方面不是有效图像或空值）。

现在我正在使用 Postman，但理想情况下我想要一个应用程序来呈现这个图像。

任何想法我做错了什么？我尝试使用 base64 编码和其他东西，但似乎没有任何效果。

谢谢！

Answer 1

这样您就可以从S3存储中以流的形式检索文件

public async Task<Stream> ReadObjectData(MediaFolder key, String fileName)
{
    try
    {
        using (var client = new AmazonS3Client(accessKey, accessSecret, endpoint))
        {
            var request = new GetObjectRequest
            {
                BucketName = bucket,
                Key = key + "/" + fileName
            };

            using (var getObjectResponse = await client.GetObjectAsync(request))
            {
                using (var responseStream = getObjectResponse.ResponseStream)
                {
                    var stream = new MemoryStream();
                    await responseStream.CopyToAsync(stream);
                    stream.Position = 0;
                    return stream;
                }
            }
        }
    }
    catch (Exception exception)
    {
        throw new Exception("Read object operation failed.", exception);
    }
}

然后 - 将此流返回为FileStreamResult：

[HttpGet("ProfilePic")]
public async Task<IActionResult> GetProfilePicture()
{
    var user = await GetUserFromBearerToken();

    Stream imageStream = await _fileService.ReadObjectData(MediaFolder.Profiles, user.ProfileImageFileName);

    Response.Headers.Add("Content-Disposition", new ContentDisposition
    {
        FileName = "Image.jpg",
        Inline = true // false = prompt the user for downloading; true = browser to try to show the file inline
    }.ToString());

    return File(imageStream, "image/jpeg");
}